The present invention relates to semiconductor power devices, and more particularly to improved trench-gate power devices and methods of manufacturing the same.
FIG. 1 is a cross section view of a conventional trench-gate MOSFET 100 which has known physical and performance characteristics and limitations such as cell pitch, break down voltage capability, on-resistance (Rdson), transistor ruggedness. Trench gate 105 extends through P-well 106 and terminates in N-epi region 104. Trench gate 105 includes a gate dielectric 114 lining the trench sidewalls and bottom, and a recessed gate electrode 112. Dielectric layers 116 and 118 insulate gate electrode 112 from overlying source interconnect (not shown).
FIG. 2 is a cross section view of a conventional dual gate trench MOSFET 200 (also referred to as shielded gate trench MOSFET) which improves on certain characteristics of trench-gate trench MOSFET 100 in FIG. 1. The trench 205 includes a shield electrode 220 insulated from the drift region 204 by a shield dielectric layer 222. Trench 205 also includes gate electrode 212 over and insulated from shield electrode 220 by an inter-poly dielectric layer 224. Shield electrode 220 reduces the gate-drain capacitance (Cgd) and improves the breakdown voltage. One drawback of both the single gate transistor 100 and dual gate transistor 200, however, is that the drift region contributes up to about 40% of the total Rdson, significantly limiting improvements in Rdson. For the dual gate trench structure, the deeper trenches exacerbate this problem by requiring even a thicker drift region. Another drawback of trench-gate transistors 100 and 200 is that the high electric field at the bottom of the trench due to the bottom trench curvature, limits improving several performance parameters such as breakdown voltage and transistor ruggedness. Some applications require integration of Schottky diode with power MOSFET. However, such integration typically requires a complex process technology with many process and mask steps.
Thus, there is a need for cost effective structures and methods for forming trench-gate FETs, monolithically integrated diode and MOSFET structures, and termination structures which eliminate or minimize the drawbacks associated with prior art techniques, thus allowing substantial improvements in the physical and performance characteristics of trench-gate FETs.